#!/bin/sh

if [ $# -lt 2 ]; then
    echo "Usage: renpart oldpart newpart [file ...]"
    echo "  to rename files matching *oldpart* -> *newpart*"
    echo "  Try all files in current directory if none specified"
    exit 1
fi  > /dev/stderr

op="$1"
np="$2"
shift 2

function rename_one {
    fn="$1"
    nfn="${fn/$op/$np}"
    echo "$fn -> $nfn"
    mv -i -- "$fn" "$nfn"
}

if [ $# = 0 ]; then
   for fn in *${op}*; do
       rename_one "$fn"
   done
else
   for fn in "$@"; do
       rename_one "$fn"
   done
fi